National Geographic : 1940 Jun
©Spence Air Photos YOU SEE EXACTLY HOW GREAT BOULDER DAM WORKS, IN THIS PICTURE MADE BEFORE LAKEMEAD WAS FILLED (SEE PAGE 762) Four windowed towers, standing in the lake, are intakes. They divert water to the powerhouse below the dam. Ifthe lake should become too full, itsoverflow would escape through giant spillways (right and left). Squirting streams show big valves being tested. The roadway over the dam crest gives wheels their first chance in history to roll between Arizona (left) and Nevada across the Colorado River. Power from Boulder Dam supplies many California cities, including Los Angeles.